This invention concerns novel paraffin conversion processes for raw paraffinic feeds of hydrocarbons carried out in the presence of crystalline zeolite material.
It has been known in art of petroleum processing to reduce the pour point of hydrocarbon oils by reducing those hydrocarbons which readily solidify (waxes) from the hydrocarbon feedstock. Previously, waxy components had been removed by means of low temperature solvent dewaxing. More recently, however, catalytic techniques have been made available for dewaxing petroleum feedstocks.
A process of that nature developed by British Petroleum is described in The Oil and Gas Journal dated Jan. 6, 1975, at pages 69-73. See also U.S. Pat. No. 3,668,113.
In U.S. Pat. No. Re. 28,398 to Chen et al. a process for catalytic dewaxing is described using a catalyst comprising zeolite ZSM-5.
U.S. Pat. No. 3,956,102 relates to a process involving the hydrodewaxing of petroleum distillates utilizing a ZSM-5 zeolite catalyst.
U.S. Pat. No. 4,247,388 to Banta et al. discloses that the catalytic performance of certain acidic zeolites such as those of the ZSM-5 type in hydrodewaxing operations is improved by controlling the alpha activity of such zeolites to within the range of 55-150, e.g., by treatment with steam. These zeolites can have the original cations replaced, preferably with cations of metals such as manganese and calcium.
U.S. Pat. No. 4,284,529 to Shihabi discloses improvements in pour point reduction by means of catalytic dewaxing employing a catalyst prepared from a ZSM-5 type zeolite having a constraint index of about 1 to 12. This dewaxing process employs a low acidity form of zeolite such as ZSM-5 or ZSM-11 in which the low acidity is imparted by steaming the zeolite to reduce its cracking activity to an alpha value of not less than about 5, followed by base ion exchange with an alkali metal cation to reduce the alpha value to not greater than 1.0. The conditions substantially eliminate the activity of the zeolite for cracking n-hexane. Shihabi indicates that the preferred forms of the zeolite contain no hydrogenation metal component. A preferred catalyst is referred to therein as a pre-steamed NaZSM-5 and is employed to dewax crude oils and other waxy feedstocks in the presence or absence of added hydrogen. These catalysts are effective at start-of-run temperature of about 640.degree. F. and exhibit excellent aging behavior in the presence of hydrogen. However, in the absence of hydrogen these catalysts exhibit a gradual aging requiring a daily increase of about 1.degree.-10.degree. F. in the reaction temperature.
U.S. Pat. No. 4,448,673 to Shihabi describes a high silica-to-alumina ratio acidic crystalline zeolite catalyst of a group, which includes ZSM-5, having increased activity. The zeolite catalyst is prepared by steaming a precursor crystalline aluminosilicate in the hydrogen or ammonium form which has an alpha value of greater than about 20 in the presence of ammonia to provide a crystalline alluminosilicate having an alpha value of from about 10 to about 150 and thereafter ion-exchanging the steamed precursor with an alkali metal cation under conditions effective to further reduce the alpha value to a negligible amount.
U.S. Pat. No. 4,510,045 to Dessau discloses a hydrodewaxing process which includes use of a non-acidic medium pore zeolite, such as ZSM-5, activated by steaming in the presence of binders such as alumina.
U.S. Pat. No. 4,229,282 to Peters et al. is concerned with dewaxing by hydrocracking through use of a nickel-tungsten zeolite catalyst system wherein the alpha value of the zeolite used in the process is at least 140 and ranges up to an alpha value of 200 or greater. The silica-to-alumina ratio in the system is approximately 70 to 1 and is unmodified by steam to reduce the alpha value.
U.S. Pat. No. 4,257,872 to La Pierre et al. involves a dual bed process for catalytic hydrocracking by passing the charge stock first over hydrotreating catalysts (which can include metals or metal oxides of Group VI B and/or Group VIII deposited on a solid porous support oxide such as alumina, titania, zirconia or mixtures thereof) in order to convert sulfur, nitrogen and oxygen derivatives of hydrocarbon to hydrogen sulfide, ammonia, and water while depositing metal contaminant from hydrodecomposition of any organo-metal compounds. The entire effluent from the hydrotreating zone is then passed to a hydrocracking zone over a zeolite catalyst, such as ZSM-5, which is in an alkali metal non-acidic form having an alpha value less than 10 and preferably less than 5. The zeolite catalyst used in this second step may be NaZSM-5.
U.S. Pat. No. 4,541,919 to La Pierre et al. relates to a process for dewaxing of heavy oils using a large pore zeolite which has been modified by coke deposition.
U.S. Pat. No. 4,518,485 to La Pierre et al. requires a 2-step dewaxing process which employs hydrotreating to remove a portion of sulfur and nitrogen compounds, followed by catalytic dewaxing with zeolite beta having a silica/alumina ratio of at least 30 and a hydrogenation/dehydrogenation component under isomerization conditions and at temperatures from 250.degree. C. to 500.degree. C.
U.S. Pat. Application Serial No. 018.112 filed February 24, 1987 now U.S. Pat. No. 4.808,296 and having a common assignee as this application discloses a catalyst composition and method for dewaxing a wax-containing hydrocarbon feedstock which includes a zeolite, especially a ZSM-5, characterized by a silica-to-alumina ratio from about 12 to about 200, a Constraint Index of from about 1 to about 12, and an alpha value of not more than about 50, in combination with a Group VIII metal hydrogenation-dehydrogenation component.
Catalytic dewaxing of the present invention involves shape selective conversion of straight and slightly branched aliphatic compounds of 12 or more carbon atoms. While conversion usually includes cracking the paraffinic components, which can reduce the yield of product having acceptable pour point because of loss of low carbon chains resulting from the cracking, the waxy component can also be reduced by isomerization of the paraffin chains, which does not affect the overall yield of an acceptable product of reduced pour point.
This latter dewaxing activity has been known to occur in the case of large pore zeolites. Large pore zeolites are typically those with a Constraint Index less than 1, or a pore opening greater than about 6-7 angstrom units. However, large pore zeolites are particularly susceptible to poisoning, such as by nitrogen or nitrogen-containing compounds, and thus can require unacceptably high temperatures of over 800.degree. F. in processing to minimize the effect of such poisoning. The processing temperature must be raised as the large pore catalyst ages to maintain catalytic activity. Furthermore, the use of currently available commercial medium pore zeolites such as Ni/ZSM-5 also requires unacceptably high temperatures and gives low yields when processing paraffinic, nitrogencontaining feeds.
It is therefore an object of the present invention to provide a more active medium pore catalyst for use in reducing the pour point of paraffinic feeds, particularly feeds with a high nitrogen content, while at the same time producing higher yields.
It is a further object of the present invention to provide a more active medium pore catalyst for reducing the pour point of paraffinic, high nitrogen content feeds at lower operating temperatures.
It is still another object of the present invention to provide a more active medium pore catalyst for reducing the pour point of paraffinic, high nitrogen content feeds while providing superior catalyst regenerability.